The operation of burners used in industrial, commercial, residential furnaces, heat treating ovens, and boilers is well recognized. The desire to operate these burners as efficiently as possible has become essential due to the escalating cost of fuel. Many different techniques and pieces of equipment are used to obtain the most efficient type of burner operation.
The chemistry of combustion is well established with mathematical formulas that accurately describe all phases of the process. In its simplest form, combustion is the combination of oxygen from the air with hydrogen and carbon from the fuel to form carbon dioxide, water, and energy (in the form of light and heat).
Perfect combustion occurs when all of the carbon and hydrogen in the fuel unites with all of the oxygen supplied by the air. For this to happen, three factors must occur. These three factors are that the temperature is high enough for the fuel/air mixture to ignite. That sufficient turbulence of the fuel and air are present to provide the necessary mixing. And, that sufficient time is allowed for the fuel and oxygen to burn. In the real world, perfect combustion is extremely difficult to achieve and the usual fuel/air ratio will not completely burn. Therefore, a controlled amount of extra or excess air is added, increasing the chance that all of the fuel will mix with oxygen in time to burn completely and minimize incomplete combustion. Incomplete combustion is costly because it produces partially burnt fuels in the form of smoke and carbon monoxide. These products escape up the flue carrying away large amounts of otherwise usable energy.
Too much excess air wastes energy also. First, energy is lost heating the incoming excess air. Second, the excess air increases the volume of heated gasses passing through the boiler. The heated gasses spend less time in the boiler and as a result transfer less energy from the combustion gases to the boiler fluid.
In an effort to minimize these losses, it has been beneficial to utilize various types of combustion analyzers. One analyzer is an A7001 Combustion Efficiency Analyzer as sold by Honeywell. The A7001 Combustion Efficiency Analyzer is used by burner service technicians to sample and analyze flue gas from various types of burners. The parameters measured include: percent of oxygen concentration in the flue gas, flue gas temperature rise, and smoke spot number. The meter also displays combustion efficiency based on flue gas oxygen content, temperature rise, and fuel properties. Service technicians use this information when adjusting burner fuel to air ratios to achieve an optimum combustion efficiency.
In certain types of applications it is also necessary to measure and adjust the optimum operation with the carbon monoxide content as one of the parameters. This is accomplished by extracting a sample of the flue gas as it passes up the stack. The sample is then chemically analyzed. The analysis can be manual or can be accomplished by extracting a carefully controlled amount of flue gas through a chemical cell. The extraction is accomplished by a hand-operated type of draw pump, and is subject to many variations due to the mode of operation of the pump.